Control flow not supported in higher order reverse mode AD

julia> using Diffractor: var"'"

julia> (x->x*x*x*x)''(1.0)
stmt = :(goto %3 if not %7)
stmt = :(goto %3 if not %7)
stmt = :(goto %3 if not %7)
stmt = :(goto %3 if not %7)
stmt = :(goto %3 if not %7)
ERROR: 
Stacktrace:
  [1] error()
    @ Base ./error.jl:42
  [2] transform!(ci::Core.CodeInfo, meth::Method, nargs::Int64, sparams::Core.SimpleVector, N::Int64)
    @ Diffractor ~/.julia/packages/Diffractor/A8Ou2/src/stage1/recurse.jl:709
  [3] perform_optic_transform(ff::Type{Diffractor.∂⃖recurse{2}}, args::Any)
    @ Diffractor ~/.julia/packages/Diffractor/A8Ou2/src/stage1/generated.jl:25
  [4] (::Core.GeneratedFunctionStub)(::Any, ::Vararg{Any})
    @ Core ./boot.jl:580
  [5] (::Diffractor.∂⃖{2})(::typeof(Base.afoldl), ::Function, ::Vararg{Any})
    @ Diffractor ~/.julia/packages/Diffractor/A8Ou2/src/stage1/generated.jl:218
  [6] (::Diffractor.∂⃖{2})(::typeof(Core._apply_iterate), ::Function, ::Function, ::Tuple{typeof(*), Float64}, ::Vararg{Union{Tuple, NamedTuple}})
    @ Diffractor ~/.julia/packages/Diffractor/A8Ou2/src/stage1/generated.jl:364
  [7] *
    @ ./operators.jl:655 [inlined]
  [8] ∂⃖
    @ ~/.julia/packages/Diffractor/A8Ou2/src/extra_rules.jl:85 [inlined]
  [9] #1
    @ ./REPL[2]:1 [inlined]
 [10] ∂⃖
    @ ~/.julia/packages/Diffractor/A8Ou2/src/stage1/generated.jl:218 [inlined]
 [11] ∂⃖
    @ ~/.julia/packages/Diffractor/A8Ou2/src/stage1/generated.jl:61 [inlined]
 [12] PrimeDerivativeBack
    @ ~/.julia/packages/Diffractor/A8Ou2/src/interface.jl:157 [inlined]
 [13] (::Diffractor.∂⃖recurse{1})(::Diffractor.PrimeDerivativeBack{1, var"#1#2"}, ::Float64)
    @ Diffractor ~/.julia/packages/Diffractor/A8Ou2/src/stage1/generated.jl:0
 [14] ∂⃖
    @ ~/.julia/packages/Diffractor/A8Ou2/src/stage1/generated.jl:211 [inlined]
 [15] (::Diffractor.PrimeDerivativeBack{2, var"#1#2"})(x::Float64)
    @ Diffractor ~/.julia/packages/Diffractor/A8Ou2/src/interface.jl:157
 [16] top-level scope
    @ REPL[2]:1

Start by reproducing the higher-order reverse-mode example and read the transform! entry point in src/stage1/recurse.jl around line 709, along with the generated.jl and interface.jl frames shown in the stack trace. Done means the reported control-flow case no longer fails during transformation and produces the expected result.